pension contribution

I believe with an IRA there is the mailbox rule meaning, on July 15 i could file a return, deduct 5k for an IRA
where the taxpayer mailed the check for 5k on 7/15 to his brokerage house.

Is that correct, and if so, can the same be done for a pension match.

I need to file a return today; can the taxpayer mail his pension match for his Sch C today prior to the filing
and be compliant - meaning he gets the pension deduction on his 2019 return?

Per the IRS website:

You must deposit contributions for a year by the due date (including extensions) for filing your federal income tax return for the year. If you obtain an extension for filing your tax return, you have until the end of that extension period to deposit the contribution, regardless of when you actually file the return.

you can file the return today. the pension contribution must be made by the extended due date of the tax return: presumably October 15th since you're talking about a Schedule C.

Very interesting - thank you....is that for 401k's and/or a SEP for a sole proprietor?

Yes for 401 K's and Sep IRA contribution can be made by October 15 as long as you have an approved extension .However for Traditional IRA's contributions must be made by April 15th .For this year special provisions to July 15